Journal of Alloys and Compounds 622 (2015) 535–540 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom Magnetic, magnetocaloric and critical properties of Ni50ÀxCuxMn37Sn13 rapidly quenched ribbons Do Tran Huu a, Nguyen Hai Yen a, Pham Thi Thanh a, Nguyen Thi Mai b, Tran Dang Thanh b,c, The-Long Phan c, Seong Cho Yu c,⇑, Nguyen Huy Dan a,⇑ a b c Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Viet Nam Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Hanoi, Viet Nam Department of Physics, Chungbuk National University, Cheongju 361-763, South Korea a r t i c l e i n f o a b s t r a c t Article history: Received 23 September 2014 Received in revised form 12 October 2014 Accepted 24 October 2014 Available online November 2014 Magnetic, magnetocaloric and critical properties of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) rapidly quenched ribbons have been studied The substitution of Cu for Ni clearly effects on magnetic transitions, magnetocaloric effects and magnetic orders of these alloy ribbons With increasing the Cu-concentration, the martensitic–austenitic phase transition shifts to lower temperature, from 265 K (for x = 0) to 180 K (for x = 4), and disappears with x = 8, while the Curie temperature, TC, is almost unchanged Both the conventional and inverse magnetocaloric effects are observed The obtained values for the maximum inverse magnetic entropy changes, |DSm|max, of the ribbons are relatively large, 5.6 J kgÀ1 KÀ1 (for x = 0) and 5.4 J kgÀ1 KÀ1 (for x = 4) with the external magnetic field change DH = 12 kOe The critical parameters (TC, b, c and d) of the ribbons are determined from the static magnetic data at the second order ferromagnetic–paramagnetic transition by using both the Arrott–Noakes and Kouvel–Fisher methods The results reveal that the long-range ferromagnetic order in the alloy is tendentiously dominated by increasing the Cu-concentration Ó 2014 Elsevier B.V All rights reserved Keywords: Magnetically ordered materials Rapid-solidification Phase transitions Magnetocaloric Introduction Magnetocaloric effect (MCE) is defined as the heating up or cooling down a magnetic material by an applied magnetic field Magnitude of MCE can be determined by direct measurement of adiabatic temperature change (DTad) or indirect measurement of magnetic entropy change (DSm) [1] Historically, MCE was first discovered by Warburg [2] in 1881, basing on the temperature change of iron in an applied magnetic field After that, the first MCE theory and device were established by Bitter, Giauque and Mac Dougall [3,4], who used the MCE of paramagnetic Gd2(SO4)3Á8H2O salts to achieve the temperature less than K In 1997, the achievement of the giant magnetocaloric effect (GMCE) in Gd–Si–Ge alloys around 300 K [5] manifested application potential of magnetic refrigeration technology at room temperature, which promised for a new generation of solid refrigerant, energy-saving and environmental protection chillers That leads to great interest in researching magnetic materials possessing large magnetic phase transitions around room temperature because of the closely ⇑ Corresponding authors E-mail addresses: (N.H Dan) scyu@chungbuk.ac.kr (S.C http://dx.doi.org/10.1016/j.jallcom.2014.10.126 0925-8388/Ó 2014 Elsevier B.V All rights reserved Yu), dannh@ims.vast.ac.vn relationship of magnetic transitions with GMCEs Such kinds of the material include Gd-containing compounds (Gd–Ge–Si) [5,6], Ascontaining alloys (Mn–As) [7], La-containing alloys (La–Fe–Si) [8], Heusler alloys (Ni–Mn–Sn, Ni–Mn–Ga, Ni–Mn–In) [9–12] and ferromagnetic perovskite manganites (La–Ca–Mn–O) [13,14] There are some material families which can exhibit both the first- and second-order magnetic phase transitions and thus both the inverse and conventional GMCEs can be respectively obtained Due to the coexistence of both the first-order and second-order magnetic transitions around room temperature, Ni–Mn–X (X = Sn, Sb, Ga and In) Heusler alloys have been attractive to research for GMCEs Besides that, so many theoretically and experimentally investigations on these alloys have been carried out for other application potentials such as shape memory effect, giant magnetoresistance, and high spin polarization [15–18] Particularly, the interesting magnetic properties of nonstoichiometric Ni–Mn–Sn have been concentratedly researched because of exhibiting large value of adiabatic temperature (DTad) and magnetic entropy (DSm) changes [13,20] In recent years, the substituting some other elements such as Ag, and Co for Ni or Mn on ferromagnetic Ni–Mn–Sn based Heusler alloys have been extensively studied to change magnetic interaction, Curie temperature and martensitic–austenitic phase transition [19–21], and to enhance magnetocaloric effect [21,22] 536 D.T Huu et al / Journal of Alloys and Compounds 622 (2015) 535–540 By using melt-spinning process to fabricate Ni–Mn–Sn based Heusler alloys, the magnetization and magnetocaloric effect of samples can be considerably improved [23–26] In this work, we investigated magnetic, magnetocaloric and critical properties of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) ribbons prepared by melt-spinning method space group [22] In order to crystalline structure with Fm3m investigate the influence of Cu-concentration on the structure of the alloy, the change of lattice constant (a) and average size (d) of crystallites was calculated by using Scherrer–Debye’s formula: Experiment X-ray diffraction patterns of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) alloy ribbons are presented in Fig 1(a) All of the samples exhibit two main (2 0) and (4 0) diffraction peaks of (Ni,Cu)2MnSn phase corresponding to basic index of L21-austenitic where d – size of the crystallites, k – wavelength of the X-ray radiation, h – Bragg angle, k – shape factor of 0.9 and b – peak width measured at half of maximum intensity It is easily seen in Fig 1(a) that the full width at half maximum of diffraction peak of all the Cu-doped (x = 1, 2, and 8) samples is larger than that of the undoped (x = 0) one The results in Fig 1(b) show that by substituting Cu for Ni, the lattice constant of Ni50ÀxCuxMn37Sn13 alloy is slightly raised up This probably is due to the larger lattice constant of Cu2MnSn crystalline phase (a = 6.17 Å) in comparison with that of Ni2MnSn phase (a = 6.05 Å) [27] The average crystallite size, which is calculated basing on the (2 0) diffraction peaks, decreases from 22.8 to 7.6 nm with increasing Cu-concentration from to at% The change of the lattice constant and average crystallite size might affect on magnetic properties of the alloy as presented below Fig 2(a) exhibits hysteresis loops of the Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) ribbons at room temperature All the samples Fig (a) XRD patterns, (b) lattice constant and average crystallite size of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) alloy ribbons (the solid lines are to guide to eyes) Fig (a) Hysteresis loops of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) ribbons (the inset enlarges the typical loops at low magnetic field); (b) thermomagnetization curves of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) ribbons measured in magnetic field of 12 kOe Cu-doped Ni50ÀxCuxMn37Sn13 pre-alloys (x = 0, 1, 2, and 8) were initially fabricated by arc-melting technique from pure elements (99.9%) of Ni, Cu, Mn and Sn in argon environment The pre-alloys were turned over and arc-melted five times to ensure their homogeneity These ingots were then melt-spun on a single roller system with a velocity of the copper roller of 40 m/s to obtain alloy ribbons Thickness of the ribbons is about 30 lm Structure of the Ni50ÀxCuxMn37Sn13 alloy ribbons was examined by powder X-ray diffraction (XRD) technique using Cu Ka radiation with measuring step of 0.02° at room temperature Magnetic properties of the ribbons were investigated by magnetization measurements on a vibrating sample magnetometer (VSM) Result and discussion dẳ kk b cos h 1ị D.T Huu et al / Journal of Alloys and Compounds 622 (2015) 535–540 537 behave as the soft magnetic material with a low coercive force less than 10 Oe (see inset of Fig 2(a)) In Fig 2(b), the temperature dependence of magnetization of the Ni50ÀxCuxMn37Sn13 ribbons with an applied magnetic field H = 12 kOe in the temperature range from 100 K to 380 K is showed The thermomagnetization curves of these samples reveal that there is an appearance of magneto-structural phase transition, or martensitic–austenitic (M–A) phase transition [10,25,28] The M–A phase transition temperature is decreased from 265 K (x = 0) to 180 K (x = 4) with increasing Cu-concentration As presented in [25], when increasing Snconcentration by 1%, the TM–A of the Ni50Mn37ÀxSn13+x alloy ribbon is rapidly decreased from 265 to 165 K The substitution of Cu for Ni in the Ni50ÀxCuxMn37Sn13 ribbon alloys makes the TM–A decrease more slowly from 265 to 180 with increasing Cu-concentration from to at% Our obtained results can be promised to produce Ni50ÀxCuxMn37Sn13 multi-layer refrigerant for applying to the magnetic refrigeration technology While the TM–A of the alloy is strongly influenced by Cu-concentration, the Curie temperature of the austenitic phase is almost unchanged (Fig 2(b)) This can be explained by the dependence of the Curie temperature on the exchange interaction in the materials In the Ni50ÀxCuxMn37Sn13 alloy ribbons, the ferromagnetic exchange interaction of the transition metal atoms of Ni and Mn essentially decides value of their Curie temperature The substitution of Cu for Ni almost does not influence on the exchange interaction of Ni and Mn atoms resulting in no large change of the Curie temperature of the austenitic phase In order to calculate the magnetic entropy change (DSm) of the alloy ribbons, the series of M(H) curves were determined at various temperature around the first-order and second-order magnetic phase transition temperatures (Fig 3(a)) The DSm values of the Ni50ÀxCuxMn37Sn13 alloy ribbons were indirectly calculated from M(H) data by using the following Maxwell’s relation: D Sm ¼ Z H2 H1 @M @T dH ð2Þ H Fig shows DSm(T) curves with magnetic field change DH = 12 kOe of the Ni50ÀxCuxMn37Sn13 (x = and 4) ribbons Both the inverse (IMCE) and conventional (CMCE) magnetocaloric effects are revealed on the DSm(T) curves The peak of IMCE is shifted to lower temperature from 264 K to 183 K with increasing the Cu-concentration from to at%, and the maximum values of the inverse magnetic entropy change, |DSm|max, are 5.6 J kgÀ1 KÀ1 (for x = 0) and 5.4 J kgÀ1 KÀ1 (for x = 4) In accordance with Biswas et al [34], the DSm quantity follows the power law DSm $ Hn with n $ for Heusler alloys, our estimated |DSm|max values for the Ni50ÀxCuxMn37Sn13 (x = and 4) alloy ribbons are greater than 20 J kgÀ1 KÀ1 with magnetic field change DH = 50 kOe Thus, our materials have exhibited GMCE in comparison with that of the Ni50Mn37Sn13 ingot (|DSm|max = 18 J kgÀ1 KÀ1) [9] and the Gd5Si2Ge2 alloy (|DSm|max = 19 J kgÀ1 KÀ1) [5] and had a potential for application of magnetic refrigeration As for CMCE, the peak of DSm(T) is happened near room temperature and just slightly changed with the variation of Cu-concentration Although the conventional |DSm|max values are smaller, about 1.4 J kgÀ1 KÀ1 (for x = 0) and 1.2 J kgÀ1 KÀ1 (for x = 4), than those of the inverse ones, the values of full width at half maximum (FWHM) of the conventional entropy change peak are relatively large, about 39 K (for x = 0) and 30 K (for x = 4), in comparison with those of the inverse ones The refrigerant capacity, RC, of the material can be estimated by using the following relation: RC ¼ jDSm jmax  FWHM Fig (a) M(H) curves of Ni46Cu4Mn37Sn13 (x = 4) alloy ribbons around the firstorder (dash lines) and second-order (solid lines) transitions; (b) Arrott plots for the Ni46Cu4Mn37Sn13 (x = 4) alloy ribbons Fig DSm(T) curves of Ni50ÀxCuxMn37Sn13 (x = and 4) ribbons with magnetic field change DH = 12 kOe ð3Þ The calculated values of the conventional and inverse RC (with DH = 12 kOe) of the Ni50ÀxCuxMn37Sn13 alloy ribbons are 55 J kgÀ1 and 28 J kgÀ1 (for x = 0), 36 J kgÀ1 and 22 J kgÀ1 (for x = 4), respectively To clearly understand the magnetic orders at the second order phase transition (SOPT), the Arrott plots or M2–H/M plots are constructed from M(H) data (Fig 3(b)) Because the ferromagnetic– paramagnetic transition at Curie temperature is a continuous 538 D.T Huu et al / Journal of Alloys and Compounds 622 (2015) 535–540 phase transition, the power law dependence of spontaneous magnetization Ms(T) and inverse initial susceptibility vÀ1 (T) on reduced temperature e = (T À TC)/TC with the set of critical exponents of b, c, d, etc., can be determined by using the following ArrottNoakes relations [29,30]: M S Tị ẳ M0 eịb e < 0; 4ị c v1 ẳ H =M Þe e > 0; ð5Þ At Curie temperature TC, the exponent d is determined by the relation of magnetization and applied magnetic field: H ¼ DM1=d e ¼ 0; ð6Þ where M0, H0/M0 and D are the critical amplitudes The spontaneous magnetization Ms(T) and initial inverse susceptibility vÀ1 (T) of the material can be obtained from constructing and linearly fitting of Arrott plot of M2 versus H/M at high magnetic field The values of Ms(T) and vÀ1 (T) as functions of temperature T are plotted for the Ni50ÀxCuxMn37Sn13 samples with x = and In accordance with Eqs (4) and (5) for Ms(T) and vÀ1 (T), the power law fits are used to extract b, c and TC (Fig 5(a and b)) With the Ni49Cu1Mn37Sn13 alloy ribbon, the continuous power law fittings for Ms(T) and vÀ1 (T) give the critical values of b = 0.442 ± 0.005, TC = 305.03 ± 0.48 and c = 1.183 ± 0.08, TC = 304.83 ± 0.07, respectively (Fig 5(a)) Fig Temperature dependence of spontaneous magnetization Ms(T) and inverse initial susceptibility vÀ1 (T) along with fittings to Arrott–Noakes relations for Ni50ÀxCuxMn37Sn13 ribbons with (a) x = and (b) x = Similarly, for the Ni46Cu4Mn37Sn13 alloy ribbon, those values are b = 0.480 ± 0.011, TC = 314.19 ± 0.04 and c = 0.876 ± 0.011, TC = 314.22 ± 0.31 (Fig 5(b)) In comparison with some standard models such as mean field theory (b = 0.5, c = and d = 3.0), 3D-Heisenberg model (b = 0.365, c = 1.336 and d = 4.8) and 3D-Ising model (b = 0.325, c = 1.241 and d = 4.82) [32], our critical parameters attained in this method fall between those of mean field and 3D-Heisenberg models However, the critical parameters of the alloy with x = are closer to those of the mean field theory of long-range ferromagnetic orders By using Kouvel–Fisher (KF) method [31], the critical exponents can be obtained more accurately From the critical exponents determined from Arrott–Noakes relations, the plots of M1/b versus [H/ M]1/c can be constructed at various temperature Again, the values of Ms(T) and vÀ1 (T) are determined from interception of linear extrapolation of these plots with M1/b and [H/M]1/c axes, respectively The slopes of 1/b and 1/c are determined by using these equations: Ms TịẵdM s Tị=dT ẳ T T C ị=b 1 v1 ẳ T T C ị=c Tịẵdv0 Tị=dT 7ị 8ị Fig shows the KF plots with the critical parameters obtained from fittings, b = 0.449 ± 0.033, TC = 305.67 ± 0.14 K (to Eq (7)) and c = 1.192 ± 0.025, TC = 305.46 ± 0.20 K (to Eq (8)) for x = 1, Fig Kouvel–Fisher plots for spontaneous magnetization Ms(T) and inverse initial susceptibility vÀ1 (T) of the samples with (a) x = and (b) x = 539 D.T Huu et al / Journal of Alloys and Compounds 622 (2015) 535–540 and b = 0.489 ± 0.018, TC = 314.07 ± 0.24 K (to Eq (7)) and c = 0.881 ± 0.021, TC = 314.06 ± 0.13 K (to Eq (8)) for x = We can realize that these critical parameters are in good agreement with those obtained from Arrott–Noakes method The value of b parameter of the Ni49Cu1Mn37Sn13 sample is still smaller than that of Ni46Cu4Mn37Sn13 sample The value of d parameter can be obtained by fitting isothermal magnetization at T % TC to Eq (3) From linear fitting the log–log plots of M(H) at T = 305 K for x = and T = 314 K for x = 4, the d values are respectively determined as 2.857 and 3.584 The Wildom scaling Eq (9) can be also used to evaluate the accuracy of fitting process [33]: d ẳ ỵ c=b 9ị From the values of b and c of our above obtained results, values of d are calculated to be 2.802 and 3.660 for x = and 4, respectively The values of d obtained from the two methods are quite in good agreement The reliability of the obtained critical parameters can be verified by using the static-scaling theory, which predicts that the isothermal magnetization is a universal function of e and H: Mjejb ẳ f ặ Hjejbỵcị ị 10ị Here, f+ for T > TC and fÀ for T < TC are regular analytical functions From the values of b and c, which we obtained above, the static-scaling plots of M/eb versus H/eb+c in log scale are constructed Table Influence of Cu-concentration (x) on lattice constant (a), average crystallite size (d) coercive force (Hc), martensitic–austenitic transition temperature (TM–A), maximum inverse magnetic entropy change (|DSm|max) and critical parameters (TC, b, c, d) of the Ni50ÀxCuxMn37Sn13 rapidly quenched ribbons x (at%) a (Å) d (nm) Hc (Oe) TM–A (K) |DSm|max (J kgÀ1 KÀ1) TC (K) b 5.994 22.8 2.5 265 5.6 – – – – 6.000 10.2 231 – 305.5 0.448 1.192 2.857 6.000 7.7 204 – – – – – 6.015 7.5 6.5 180 5.4 314 0.489 0.811 3.584 6.005 7.6 – – – – – – c d in Fig 7(a) and (b) for x = and 4, respectively The two parts of the plots at T > TC and T < TC are separate The falling of data on the two separated branches exhibits characteristic of continuous phase transitions and proves the reliability of our achieved critical parameters The obtained results can be used to explain the variation of the M–A phase transition on the Cu-doped samples As presented in Ref [25], the Ni50Mn37Sn13 ribbon shows short-range ferromagnetic orders (b = 0.385 ± 0.035) of the ferromagnetic exchange interaction By substituting Cu for Ni in alloy, the TM–A of the Ni50ÀxCuxMn37Sn13 alloy shifts to lower temperature with increasing x That means the austenitic phase with long-range ferromagnetic orders is enhanced by Cu-concentration This might be due to the stronger covalent hybridization between the d-states of Cu and Mn atoms in comparison with that of Ni and Mn atoms [27] Therefore, ferromagnetic exchange interaction of the Ni50ÀxCuxMn37Sn13 alloy ribbons is changed from short-range to long-range by substituting Cu for Ni As a brief summary of the influence of Cu-concentration on the Ni50ÀxCuxMn37Sn13 rapidly quenched ribbons, the obtained parameters of the structure and properties are listed in Table Conclusion By substituting Cu for Ni of Ni50ÀxCuxMn37Sn13 (x = 0, 1, 2, and 8) ribbons, the lattice constant is slightly increased with increasing Cu-concentration, while the average crystalline size are strongly decreased All the alloy ribbons exhibit soft 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Cu for Ni As a brief summary of the influence of Cu-concentration on the Ni50ÀxCuxMn37Sn13 rapidly quenched ribbons, the obtained parameters of the structure and properties are listed in Table... of Ni50ÀxCuxMn37Sn13 (x = and 4) ribbons with magnetic field change DH = 12 kOe ð3Þ The calculated values of the conventional and inverse RC (with DH = 12 kOe) of the Ni50ÀxCuxMn37Sn13 alloy ribbons